They say the 24-year-old beauty is setting a shocking example to her young fans because she is riding illegally through dark streets without lights or reflectors and is not wearing a helmet.

Roger Geffen, of the national cyclists’ organisation CTC, said: “Clearly, riding at night without lights is not something we could condone...it’s illegal.”

And a spokesman for the Royal Society for the Prevention of Accidents said: “Unfortunately, advertisers do forget sometimes to make sure they are showing safe and legal behaviour when someone is using the road in an advert.”

Road safety charity Brake, which campaigns for all cyclists to wear helmets, said: “We would like to see advertisers think about safety implications and what message they are sending out. Adverts which show people not belting up or cycling without lights may send the wrong messages out to viewers.”

The ad premiered last week after Duffy conquered the Brits by winning Best Female, Best Album and Best Breakthrough Act awards.

Wearing tiny shorts, tights and a close-fitting top, she is seen jumping on to a racing bike just before a stage appearance.

Supping Diet Coke at the start and end of her trip and singing I’ve Gotta Be Me, she cycles through streets, a car park and a supermarket.

The Mercy singer said: “I drink so much Diet Coke, they were either going to give me shares in the company or put me in the advert!

“I love the ad’s attitude. My way to rebel on tour is to take off on my own and turn my phone off.”

A spokesman for Coca-Cola said: “The advert is a fictional depiction of how Duffy might take some time out and is not intended to be a real-life scenario.

“Diet Coke would urge all road users, including cyclists, to adhere to the Highway Code and to follow safety advice from government and other relevant agencies.”